Data in a data format that can be easily automatically read and processed (or identified, recognized and extracted) by a computer, without human intervention, including individual statements of fact, and their internal structure, while ensuring no semantic meaning is lost. Examples of file formats are CSV, JSON, XML, etc. Machine-readable data must be structured data. 

Non-digital material (printed or hand-written documents) is by its non-digital nature not machine-readable, as well as digital material in certain file formats, as a PDF document containing tables of data, but they are (Compare →) human-readable. The equivalent tables in a format such as a spreadsheet would be machine readable.

As another example scans (photographs) of text are not machine-readable (but are human readable!) but the equivalent text in a format such as a simple ASCII text file can machine readable and processable.

The appropriate machine-readable format may vary by type of data - so, for example, machine readable formats for geographic data may differ from those for tabular data. Sources: ODH and US OD and OD Directive

There are two types of machine-readable data: human-readable data that is marked up so that it can also be understood by computers, for example microformats or RDFa; data formats intended principally for computers, for example RDF, XML and JSON.

Source: EU OD